Machine-tool in particular with parallel architecture accommodating deformed articulations

ABSTRACT

The invention concerns a very high-speed machining machine-tool (M) consisting of a parallel structure including link bars ( 100 ) whereof one first end ( 110 ) is linked to a mobile member ( 200 ) supporting at least a tool and whereof the second end ( 120 ) is linked to at least means ( 300 ) setting it in motion relative to a frame (B). The said machine-tool is characterized in that the linkages ( 400 ) to the ends ( 100  [sic, should be  110.— Translation Editor) and  120 ) of the said bars ( 100 ) consist in an association of fictitious pivots ( 410, 420, 430 ) so as to form a joint whereof the degrees of freedom enable the parallel structure to be set in motion. The said feature enables to avoid all drawbacks related to ball linkages. The invention is applicable to high-speed machining.

AREA OF APPLICATION OF THE INVENTION

[0001] The present invention relates to the field of machine-tools forvery high-speed machining with a parallel structure and, specifically,to adaptations that permit guidance of the constituting elements of thesaid parallel structure.

DESCRIPTION OF THE PRIOR ART

[0002] A machine-tool for very high-speed machining as described inPatent Application No. WO 99/61198 in the name of the Applicant andillustrated in FIG. 1, classically comprises bars which link the meansof setting in motion and the mobile member to be set in motion. Withinthe framework of the machine-tool illustrated, the function of thesebars is to assure transformation of movements in three paralleldirections into movements in three orthogonal directions.

[0003] In order to permit and guide the plurality of movements which mayoccur in such a parallel structure, the said bars are classicallyequipped, at their ends, with joints that permit rotation along at leasttwo axes. Nevertheless, since the displacement has to be realizedisostatically, the multiplication of these linkages requires joints ofthe universal type to permit additional rotation in the axis of the saidbars.

[0004] These linkages or these joints are today produced by means thatutilize rolling balls. Now, these means have several disadvantages, themajor ones of which are described below.

[0005] Ball linkages require constant maintenance and within theframework of very high-speed machining they can provide only a limitedlifetime due to the fact of creation of a larger and larger play duringoperation. As a matter of fact, very high-speed machining has thedisadvantage of causing premature wear of the classical guidance meansby surface corrosion (tribological degradation).

[0006] This is in part due to the high dynamic stresses imposed by thevery high-speed machining which causes a high-frequency vibrationalphenomenon on the parallel structure and therefore on the elementsconstituting it.

[0007] This premature wear is difficult to express in quantitative termsand requires the users of such machine tools to change the pieces thatare liable to be worm, regularly and prematurely. Such a replacement ofall the joints of a machine-tool for high-speed machining with parallelstructure implies immobilization of the structure, stopping the chain ofmanufacture in which it participates, carrying out new precision testsbefore start-up, etc.

[0008] The precision criteria in the machining carried out today, suchas the lack of rigidity of the parallel structure due to wear of theclassical means of guidance or linkage is difficult to tolerate. At thesame time, the time of immobilization and the cost of replacementinherent in this type of linkage and application have a considerablysevere effect on the operating budget of such a machine-tool.

[0009] The absence or slowing down of the wear and rigidity of thelinkages are criteria to which fictitious pivots respond. These joints,frequently limited to a single degree of freedom (a rotation), utilizethe controlled deformation of a material to provide the required angularfreedom. Thus, for example, the joints described in Patent ApplicationsEP 0 459 057, FR 2 738 602, DE 195 39 581, CH 375 959, U.S. Pat. No.2,950,079, FR 2 666 630, U.S. Pat. No. 4,297,904, define fictitiouspivots , based on the deformation of the linkage zones between a fixedpart and a mobile part.

DESCRIPTION OF THE INVENTION

[0010] Starting from this state of affairs and starting frompre-established specifications, the Applicant carried out research whichled to the conception and realization of a machine-tool which adopts atechnological solution that permits elimination of the disadvantagesinherent in the lack of rigidity of parallel structures, by exploitingand adapting the characteristics of fictitious pivots.

[0011] This machine-tool for very high-speed machining is of the typeconsisting of a parallel structure comprising linkage bars, the firstend of which is linked to a mobile member supporting at least one tooland the second end is linked to at least one means for setting in motionrelative to a frame.

[0012] According to the main characteristic of the invention, thelinkages at the end of the said bars are constituted by a combination offictitious pivots so as to form a joint, the degrees of freedom of whichenable the parallel structure to be set in motion.

[0013] The utilization of a combination of fictitious pivots isparticularly advantageous in that this type of linkage functions bydeformation of material and thus permits a greater rigidity of the jointwhile still permitting movement. Similarly, a combination of fictitiouspivots permits not only the said movements with a greater rigidity butalso allows torsion, which avoids the utilization of universal-typejoints.

[0014] Moreover, this type of joint does not require special maintenancedue to the fact that the joint is not made by guidance or friction. Notribological degradation is to be feared, contrary to the classicallyused ball linkages. The consequences of these characteristics is thatthe machine-tool of the invention will have better precision than thealready existing ones, and that its maintenance as well as its operationwill be less expensive, both with regard to time and material.

[0015] This main characteristic of the invention does not constitute asimple combination or an evident combination of two known devices. As amatter of fact, it is the new criteria of precision machining at veryhigh speeds and the decrease of the maintenance costs of specificationswhich led the Applicant to carry out these investigations. Also, theneed to which the main characteristic of the invention responds isfundamentally new.

[0016] The utilization of fictitious pivots for the guidance of armsconstituting the parallel structure of a machine-tool for veryhigh-speed machining also represents great novelty in that the designersin the field of machine tools have a tendency to design based on knownand mastered links. Thus, the realization of joints combining aplurality of fictitious pivots also constitutes a break from the normalreasoning processes of machine-tool designers.

[0017] Moreover, this characteristic does not simply combine afictitious pivot with a parallel structure but requires a combination offictitious pivots in order to satisfy the specific linking criteriaestablished by the intended application, namely, enables the setting inmotion and isostatic guidance of the arms constituting a parallelstructure, which require more than one degree of freedom.

[0018] The invention also concerns a deformation joint designed for thismachine-tool and which can also be used separately.

[0019] The fundamental concepts of the invention having been exposedabove in their most elementary form, other details and characteristicswill follow more clearly from reading the description which follows inrelation to the attached drawings, giving, as a nonlimiting example, anembodiment of a machine-tool and of a deformation joint according to theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 is a perspective view of a machine tool with parallelstructure of the technological background;

[0021]FIG. 2 is a schematic perspective view of an embodiment of a jointof a machine-tool according to the invention;

[0022]FIG. 3 is an exploded schematic perspective view of a detail ofthe joint of FIG. 2 and

[0023]FIG. 4 is a kinematic scheme of the joint of FIG. 2.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0024] As illustrated in the drawing of FIG. 1, the machine-tool forvery high-speed machining referenced M in its entirety is of the typecomprising linkage bars 100 whereof one first end 110 is connected to amobile member 200 supporting at least one tool (not shown) and whereofthe second end 120 is connected to at least one means of setting inmotion 300 relative to a frame referenced B. According to theillustrated embodiment, there are six of the said bars 100 which arelinked through their second end 120, two by two, to means of setting inmotion 200, of which there are three. The first ends 110 are linked twoby two to the same side of the mobile member 200, which is here in theform of a triangular plate, each side accepting the first end 110 of thetwo linked bars 100. Within the nonlimiting embodiment of themachine-tool M illustrated, the parallel architecture was designed sothat the separate or concerted movement of the three means for settingin motion 300 along axis Z permits rectilinear displacement along axesX, Y and Z of the mobile member 200.

[0025] According to the invention, linkages 400 at the ends of the saidbars 100 are constituted by a combination of fictitious pivots so as toform a joint, the degrees of freedom of which permit setting theparallel structure in motion.

[0026] Although this characteristic is an ideal characteristic, it ispossible for the parallel structure to be a mixed structure, namely,that only a part of the said linkages 400 is produced by a combinationof fictitious pivots. As a matter of fact, in order to reach therequired rigidity and consequently the required precision, it ispossible that a limited number of joints 400 with fictitious pivots willbe sufficient.

[0027] As illustrated in more detail in the drawing of FIG. 3, eachjoint 400 is formed by three fictitious pivots 410, 420, 430, the axesof which are perpendicular to one another.

[0028] According to a particularly advantageous characteristic of theinvention, the profile of the said linkage bars 100 is preformed so thatit will accept a torsional deformation, without reaching its elasticlimit, so that one of the fictitious pivots that forms the joint isrealized by the torsional elasticity of the bar 100 or the end of bar120 or 110 itself. This embodiment of the fictitious pivot isparticularly useful within the framework of the degree of freedom inrotation around the longitudinal axis of linkage bars 100, which untilnow was enabled with a “universal” joint. Thus, according to thenonlimiting embodiment which is illustrated, the fictitious pivot 430 isconstituted by bar 100 or the end 110 or 120 of the bar, which adopts aprofile that permits torsion according to a limited number of degrees[of freedom]. This linkage bar 100 has at least on its end 110 or 120the profile illustrated in the form of a cross, which is particularlysuitable for accepting torsional stresses. According to thetechnological choice envisaged by the Applicant, bar 100 or its end areprofiled so that it accepts a rotation of about one degree.

[0029] When the number of degrees necessary for the rotation is larger,according to an embodiment which is illustrated, but is nonlimiting, thesaid fictitious pivots 410, 420 are formed by at least one deformablesubassembly comprising a cross, in which the ends of the two first armsare linked by a first plate and the ends of the two other arms arelinked by a second plate. More precisely, the fictitious pivot 410 isformed by a cross, where the ends of the two arms 411 and 412 are linkedthrough a first plate 413 and the ends of the two other arms 414 and 415are linked by a second plate 416.

[0030] As illustrated in the drawings of FIG. 2 and FIG. 3, thefictitious pivots assure pivot linkage pairwise with the intersection ofthe cross, which constitutes the theoretical axis of rotation.

[0031] As illustrated in the kinematic scheme given in the drawing ofFIG. 4, the axes of these fictitious pivots are perpendicular to oneanother. According to the illustrated nonlimiting embodiments offictitious pivots, the latter assure a rotary linkage along about 20degrees.

[0032] Moreover, as illustrated in FIG. 2, when the machine-tool is ofthe type illustrated in FIG. 1, where the setting in motion of themobile member 200 is performed by means of three pairs of arms 100, eachpair being linked at one of their ends 120 to a single means of settingin motion 300, the said linkage bars 100 forming a pair are linked to asame first mobile crosspiece 500, which is linked by at least onefictitious pivot 420 and/or 410 to a second crosspiece 600, attached tothe said means of setting in motion 300 (not illustrated in FIG. 2).

[0033] The invention also concerns the deformation joint adapted to amachine-tool of the type illustrated but it can be applied to othermachines or devices. This joint is characterized by the fact that it isformed by a plurality of fictitious pivots, the associated degrees offreedom of which permit quasi-functioning as a trunnion. As a matter offact, the joint imagined by the Applicant has the rigiditycharacteristics and the absence of the necessity of maintenance due totribological degradations, since the fictitious pivots constituting itprovide joints without friction.

[0034] It is understood that the machine-tool and the deformation joint,which were described and represented above, were aimed at disclosurerather than limitation. Naturally, various arrangements, modificationsand improvements can be provided to the example given above withoutdeparting from the framework of the invention, taken in its broadestaspects and spirit.

1. Machine-tool (M) for very high-speed machining of the type consistingof a parallel structure comprising linkage bars (100), the first end ofwhich (110) is linked with a mobile member (200) supporting at least onetool and the second end of which (120) is linked to at least one meansof setting in motion (300) with respect to a frame (B), CHARACTERIZED BYTHE FACT THAT the linkages (400) at the ends (110 and 120) of the saidbars (100) are constituted of a combination of fictitious pivots (410,420, 430) so as to form a joint, the degrees of freedom of which permitsetting the parallel structure into motion.
 2. Machine-tool (M)according to claim 1, CHARACTERIZED BY THE FACT THAT only one part ofthe said linkages (400) is realized by means of a combination offictitious pivots.
 3. Machine-tool (M) according to claim 1,CHARACTERIZED BY THE FACT THAT each joint (400) is formed by threefictitious pivots (410, 420, 430), the axes of which are perpendicularto one another.
 4. Machine-tool (M) according to claim 1, CHARACTERIZEDBY THE FACT THAT the profile of the said linkage bars (100) is preformedso that it will accept, without reaching its elastic limit, a torsionaldeformation, so that one of the fictitious pivots (430) forming thejoint (400) is realized through the elasticity of the bar (100) itself.5. Machine-tool (M) according to claim 1, CHARACTERIZED BY THE FACT THATthe said fictitious pivots (410, 420, 430) are formed by at least onedeformable subassembly comprising a cross, in which the ends of the twoarms (411 and 412) are linked by a first plate (413) and the ends of thetwo other arms (414 and 415) are linked by a second plate (416). 6.Machine-tool (M) according to claim 1, of the type where the setting inmotion of the mobile member (200) is carried out by means of three pairsof arms (100), each of the pairs being linked at one of their ends (120)to a single means of setting in motion (300), CHARACTERIZED BY THE FACTTHAT the said linkage bars (100) forming a pair are linked to the samefirst mobile crosspiece (500), which is linked by at least onefictitious pivot (410 and 420), to a second crosspiece (600) fixed tothe said means of setting in motion (300).